Accurate measurement of proximal internal carotid artery stenosis requires clear delineation of the residual lumen within the stenotic segment. We have recently developed a technique for gadolinium enhanced 3D time resolved magnetic resonance arteriography that can accomplish this goal. The technique provides a series of 3D images with sufficient temporal resolution to separate the carotid arteries from the jugular veins. The availability of the temporal image series avoids uncertainties in injection timing relative to image acquisition and permits image subtraction in a manner completely analogous to DSA but with 3D reprojection capabilities. Subtraction of accumulated background signal from previous injection allows for multiple site studies with repeated injections. We hypothesize that with images available at all points in the contrast pass, including the peak, small doses of contrast material with permit examination of the aortic arch, cervical vessels and intracranial vessels. Specific aims include: (1) implementation of a data acquisition scheme in which a subset of each 3D data set is used to form an on-line 2D subtracted projection image which will permit selection of a subset of the entire 3D data set to be chosen for reconstruction. (2) Use of ROI data from the preview images to permit reweighting of acquired k-space volumes to reduce intra and extraluminal artifacts. (3) Investigation of temporal and spatial resolution for image of the carotid bifurcation. (4) Optimization of the dose of intravenous contrast material and the injection rate. (5) Implementation of these innovation for a blinded assessment of carotid stenosis measurement.